Linksys router drops internet connection

I am sharing the internet with 5 workstations. The isp is sbc. The dsl modem is a speedstrean 5100. The router is a linksys befvp41 with dhcp enabled. “I have a switch (linksys sd205) connecting the workstations to the router. No fileserver is involved. Using PPPoE.

The internet connection keeps dropping. If I power off the router and modem, the internet comes back. Any suggestions. Keep alive is 30 seconds. Thank You.